The invention concerns a device to cut, perforate, or inscribe repeating patterns in continuously-moving flat material, especially a sandwich material, by locally vaporizing the sheet with at least one controllable laser beam from at least one beam deflection system, wherein each laser beam is moved relative to the flat material in two perpendicular directions (x and y) from a fixed point. The invention also concerns a corresponding device.
In EP 0 357 841 A1, a device is disclosed to create predetermined separation lines/perforations with laser beams. To locally vaporize a part of one-layer or multiple-layer packaging material, there is a controllable laser beam for creating repeating images/patterns as the sheet of packaging material continuously moves. Fast changes in speed cannot be executed in the prior art procedure. The starting signal for introducing the structures are created when repeating printed images on the packaging material are detected. This causes the introduced lines/perforations to agree with the printed pattern on the sheet of material.
Since an existing printed pattern is required to control the laser scanning system in the prior art device, unprinted material cannot be processed. In addition, a faulty print on the flat material causes the laser-beam-generated line or perforation to be incorrect since it depends on the printed pattern.
In the prior art device, the surface speed is detected with an incremental, rotating shaft encoder. While the cut or perforation is being created, the focal length of the laser beam is adjusted so that the focus is always the same. Simultaneously, the recurring images on the packaging material are monitored by a feedback loop to the image-dependent control signals in order to create the notches fully aligned with the repeating patterns.
In addition, laser beam deflection systems are known per se in which the laser beam is deflected by mirror galvanometer systems that are also known per se. For example, this is the case in FR 25 76 836 A1 in which a laser system is described that is stationary in the x and y direction and can only be changed in the z direction to adjust the focal length of the laser beam.
The problem of the invention is to design and develop a procedure and device to cut or perforate repeating patterns in continuously moving flat material so that a pattern can be created which is in alignment with the bent and folded edges in unprinted material at any speed.
In particular, flat material speeds can be reached of up to 300 m/min.
In regard to the process, this problem is solved by the following steps:
Detecting the rate of the flat material, PA0 Providing bent or folded edges in the moving flat material and detecting its position. PA0 Controlling the beam deflections system so that it executes the cutting, perforation or writing process depending on a synchronization pulse generated when the bent or folded edges are detected, and the detected rate of the flat material, and PA0 Monitoring the beam position/beam intensity of each laser beam depending on the detected rate of the flat material and the detected bent or folded edges.
The bent or folded edges are created and their position can be detected in a single step as is the case with the embodiment described in the figures.
In one advantageous embodiment of the invention, the position of the generated pattern is monitored and regulated in relation to the created bent or folded edges.
In regard to the device, the problem is solved in that an element is provided to determine the speed of the flat material; at least one stamping tool is provided to introduce bent or folded edges in the moving flat material; and the stamping tool is provided with an incremental shaft encoder with which the position of the stamping tool edges is detected in reference to the flat material which creates a synchronization pulse to control the beam deflection system(s) that execute the cutting, perforation or writing procedure.
With the device according to the invention, a rate-independent, aligned relationship is created between the bend or fold pattern and the cut or laser perforation or inscription. In contrast to the above-described state of the art, the cut, perforation or inscription can be created on an unprinted flat material.
In addition, means are provided according to the invention that can monitor and regulate the position of the created pattern in relationship to the applied bent or folded edges. An image processing system is particularly suitable for this.
Connecting an incremental shaft encoder to the roller-shaped stamping tool to create bent or folded edges allows the rate of the surface to be precisely detected and allows the position of the introduced bent or folded edge to be monitored. Therefore, the position of the stamping tool over the perimeter of the roller is provided with incremental shaft encoders, and a zero position of the tool or tool edges is also defined.
With the device according to the invention, the stamping tool is located either in front of or behind the laser viewed in the direction of motion of the flat material. The local distance between the stamping tool and beam deflection system can be up to several meters. Manifestations of stretching arising in this area can be compensated by detecting differences in tension and pressure using the control computer so that a precision of .ltoreq.0.5 mm can be maintained in reference to the contour precision of the perforation figures. By varying the difference of the counted pulses of the incremental shaft encoder for the surface speed to the counting pulses of the incremental shaft encoder in the stamping tool, the structures to be created can be shifted or positioned in or counter to the direction of belt movement in 0.01 mm steps.
The process according to the invention is particularly advantageous since basically white and unprinted material can be provided with corresponding perforation figures or inscriptions that are always specifically aligned or positioned in relation to the bent or folded edges of the individual, continuously repeating packaging blanks.
In the device according to the invention, it is particularly useful to use a self-contained CO.sub.2 laser, i.e., a laser without an external gas supply. Since the laser beam is deflected from a fixed point, different focal lengths are necessary; hence the invention additionally provides that the intensity of the laser beam can be changed. This can occur within the framework of the invention by using a lens system to adjust the focal length of the z axis of the laser beam to alter the beam intensity. It is alternately possible, however, to change the laser beam intensity by influencing the power of the laser.
To detect the speed of the flat material, an incremental shaft encoder can be used or a laser Doppler anemometer.
To avoid or reduce the absorption of the laser beam by dust, another embodiment of the invention provides a vacuum hood after the laser scanning system (viewed in the direction of flat material travel) to remove the dust arising from local vaporization. This is useful for environmental reasons and especially when packaging that hold foods are created from the flat material.
The invention will be further explained in the following with reference to two preferred exemplary embodiments shown in the drawing. Shown in the drawing are: